1. Field of the Invention
The present invention is directed to wheel balancing systems, and more particularly to systems for balancing motor vehicle wheels of different sizes and types.
2. Description of the Related Art
While it is possible to envisage a wheel balancing machine designed for a given size of vehicle wheel, it will be appreciated that it is desirable to have a balancing machine which is capable of dealing with motor vehicle wheels of different sizes and types; for example, automobile wheels, motorcycle wheels and the wheels of commercial and public vehicles. That however requires the machine to be suitably adapted, for the balancing operation, to the size and type of wheel involved.
A balancing machine for motor vehicle wheels, which is designed with that aim in mind, as is to be found in German published specification (DE-AS) No 2 001 972, (corresponding to U.S. Pat. No. 3,741,016 to Hofmann) for balancing in two planes, has a total of three setting potentiometers for ascertaining the geometrical dimensions of the wheel to be balanced. A first setting potentiometer is provided for measuring the spacing between a fixed point of the machine, for example, the wall of the housing thereof, and the inner one of the two compensating planes, that is to say, the planes on the wheel to be balanced at which a balancing operation can be carried out, a second setting potentiometer is provided for ascertaining the distance between the two compensating planes, and the third setting potentiometer is provided for ascertaining a suitable compensating radius at which therefore a compensating or balancing operation can be effected on the wheel. The machine further includes a measuring device for ascertaining and displaying the unbalance magnitudes and angular values. In that machine, each setting potentiometer is connected to a sensing means for sensing the geometrical dimensions of the wheel to be balanced so that the potentiometers are automatically set. The sensing means itself comprises a sensing member in the form of a horizontally displaceable and pivotable lever with sensor or contact roller which can be applied against the rim flange of the wheel to be balanced, for the purposes of simultaneously ascertaining the distance between the compensating planes of the wheel and the compensating radius. The machine has a display device for displaying the sensed values.
Sensing devices are also used in wheel balancing machines which are commercially available (see for example the Hofmann operating instructions for the wheel balancing machine `geodyna 88/88m`, Impressum 9412145-09.86). Two measuring sensing levers of which one detects the distance between the balancing machine and the inward rim flange of the wheel and the other detects the outwardly disposed rim flange of the wheel are carried on displaceable measuring shafts which are oriented in parallel relationship with the main shaft of the machine on which a wheel to be balanced is clamped. The measurements, which are taken off, for example, by way of potentiometers, in respect of rim width, inside rim diameter and spacing of the compensating planes on the wheel, are inputted into an electronic evaluation assembly and displayed at a display device.
In known measuring and sensing arrangements for ascertaining the compensating or balancing positions, that is to say the compensating radii and planes, for the balancing weights, the procedure used involves measuring the outside of the rim and the rim diameter minus the thickness of the material of the rim. On the basis of those measurement values, fixed computation algorithms are then used for conversion to a theoretical center of gravity of the compensating weight. When using stick-on weights, more especially concealed weights which are therefore generally to be positioned within the rim dish configuration, that theoretically ascertained center of gravity does not always coincide with the actual position of the center of gravity. The reason for that are different rim contours and different thicknesses of material at the rims, which result in errors in the radius measurement operation. In addition, the rim contours are such that no weight can be applied to the theoretically ascertained location, and that gives rise to errors in terms of width.